Method and apparatus for machining of porous concrete



Sept. 15, 1964 METHOD AND APPARATUS FOR MACHINING 0F POROUS CONCRETE Filed Nov. 3. 1961 Ci) J2 0 1:1 W

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ATTORNEYS United States Patent 3,148,672 METHOD AND APPARATUS FOR MACHINING 0F POROUS CONCRETE Sverre 0. J. Fjeldstad, Blommenholm, Oslo, Norway,

assignor to Yxhults Stenhuggeri AB, a corporation of Sweden Filed Nov. 3, 1961, Ser. No. 149,924 8 Claims. (Cl. 125-9) This invention relates to a method and apparatus for machining of surfaces of brittle material, such as porous concrete, in order to obtain correct dimensions and a desirable shape.

In the porous concrete industry, recent development has been toward the use of precision-cut building elements joined by means of glue instead of mortar. This means that rigorous requirements must be placed on the dimensional accuracy of the elements. Experience shows that porous concrete elements which have passed through the final production step of treatment in autoclaves sometimes have a certain tendency to warp or to rise. Thus, the elements that originally have been satisfactorily cut no longer hold the correct dimensions or show totally plane surfaces. Such incorrect elements are rejected or used as a second assortment, because they cannot satisfactorily be used as an integral part of a glued porous concrete construction.

, In order to avoid the inclusion of such incorrectly dimensioned and irregular elements in a delivery of porous concrete, it has been necessary to individually check all the elements produced.

According to this invention it has been found that elements of porous concrete can be given a proper dimensioning and/or a surface shaping by a planing or scraping process that is done step by step by a plurality of planing irons or scraping irons used sequentially, each iron removing a very thin layer of the surface of the porous concrete element. Furthermore, if each gradually removed layer is thin enough, the edges of the elements will not crumble or break down.

It is also possible to reduce breakage by working the elements against a supporting tool. According to another object of the invention, therefore such an arrangement may be obtained by contiguously feeding the porous concrete elements continuously past the tool, such that the surface of any one element rests against the corresponding adjacent surface of the next one. It is preferable to feed the elements with their end surfaces lying close to each other. Thus, an element being treated by the planing or scraping tool will obtain support from the first end surface of the following element.

The end surface of such continuously fed elements should, preferably, have been planed beforehand.

In addition, it should also be noted that porous concrete has the property of acting as a grinding material, thereby causing a rapid wearing of the scraping tools. Consequently, a continual substitution of tools is necessary, and this causes substantial loss of time by discontinuance in operation and increased expense in the substitution or regrinding of tools.

By the present invention it has been found that this disadvantage can be eliminated, and this is done by using very thin steel ribbons stretched in suitable holders and held perpendicularly to the treated surface. These steel ribbons should have a thickness of 1 mm. or less, e.g. 0.35 mm. The edge, then, is so thin as to become selfgrinding.

According to another object of the invention the steel ribbon may be made movable in the holders. Thus, by a continuous, or preferably, a gradual moving of each ribbon, new sections of each ribbon are steadily brought into operation for an elfective treatment of the upper Ice surfaces of the porous concrete elements. Therefore, without a stoppage in the operation, the concrete elements can be continuously treated by fully effective cutting or scraping edges.

Where desired, the edge of the steel ribbon may he toothed, wavy or of another special shape. The holders gripping the ribbon may through a mechanical device be made to oscillate transversely to the movement of the concrete elements. In this way, the concrete elements may be provided with side surfaces having ornamental strip or wavelike lines.

For a better understanding of the invention, reference is made to the various embodiments schematically shown in the accompanying drawing, wherein:

FIG. 1 is a schematic side-view of the method and apparatus of forward feeding and treatment of porous concrete elements according to the invention.

FIG. 2 is a schematic section taken on line IIII of FIG. 1.

FIG. 3 is a side-view of the design of a treating tool according to the invention.

FIG. 4 is a top-view of a detail of the treating tool according to the invention.

FIG. 5 shows a design detail of the tool.

A suitable form of feeding according to the invention is shown in FIGS. 1 and 2. The porous concrete elements 1 are fed continuously with their end surfaces contiguous to each other, such that each element being treated is supported by the leading surface of the following element. The planing treatment itself is performed on all the four side surfaces by the planing or scrapping irons, which are arranged in two or, preferably, more steps. In the drawing three such steps have been noted 3, 3", 3", each one of which removes a very thin layer from the surfaces of each element.

Because the elements are fed on a diagonal (see FIG. 2), there is the additional advantage that the material taken away by the planing or the scraping irons will fall from the surfaces of all the elements and can be collected on a waste removal system such as a conveyor belt (not shown). Furthermore, the material removed by planing takes the form of small particles rather than dust. Thus, the small particle waste can fall from the scraping operations and be collected.

With the method shown all the concrete elements, fed via the roller way 2, will successively be subject to a dimension control as they pass through the device. If an element has the right dimensions its upper surface will not be affected by the planing or scraping irons. However, if one or two upper surfaces through swelling or wrapping of the element, are not plane, or the element is wrongly dimensioned, the three successive treating tools 3', 3", 3', will come into function and the element passes outwith a corrected shape to the right in FIG. 1.

While the planing or scraping process is performed along the element, only the rear edge has a danger of breakage. The rear edges, however, are fully supported by the leading surfaces of the respective following elements.

To ensure a tight contiguous engagement of the end surfaces it is advantageous to plane these surfaces beforehand.

Because the planing or scraping process causes a great wearing of the two edges, the present invention provides for the use of a tool which does not necessitate continual substitution. Such a planing or scraping tool takes the form of a very thin ribbon or spring steel or similar material. For example, a spring steel ribbon of .35 millimeter thickness has proved particularly advantageous, in that such a ribbon is self-grinding.

FIG. 3 discloses a means for holding a thin ribbon 13 in a suitable holder. The holder consists of a base port member 4 cut oif at its lower surface 5. A resilient holda ing member 6 keeps the scraping ribbon 13 against the support 4, the resilient member 6 being fixed to the support member 4 by a screw 7 near its center.

At the upper end of the resilient member 6 there is provided an eccentric 9 rotatable around the axis 10 in the support member 4. In the position shown in FIG. 3 the scraping tool is loosely held by the resilient member 6, and a turning of the eccentric 9 will provide a secure holding of the scraping ribbon 13.

When the scraping tool 13 is worn down through the regrinding process, it may be adjusted downwardly and restretched. Alternatively, the downward adjusting of the ribbon 13 may be accomplished by a suitable adjusting gear mechanism of a known type (not shown).

FIG. 4 discloses another preferred form of the scraping tool. Here, the thin flexible ribbon 14 is stretched between suitable holders 11 and 12, and the ribbon 14 is movable between the holders transverse to the direction of movement of the concrete blocks 1 and 1'. The ribbon 14 has suflicient length to be wound on both sides around suitable drums 15 and 16, and the transverse movement and tensioning of the ribbon 14 can be accomplished by suitable drive means to the drums 15 and 16.

FIG. 6 shows a detail of a scraping iron according to the invention. Wherein the edge 17 of the tool is wavy. The porous concrete is then provided with a wavy profile which may be of value as a decoration. It is also possible to provide means to oscillate the scraping iron 3 longitudinally as is noted by the arrow 2. The wavy edge 17 will then give a corresponding wavy pattern to the upper surface of the porous concrete element.

In the shown examples the scraping iron has been presupposed to be perpendicular to the upper surface of the porous concrete element. This arrangement has proved advantageous for most cases, but there may be some cases in which it would be practical to use the scraping iron in an oblique position, thereby letting it act like the bit of a plane.

I claim:

1. A method of accurately machining the faces of blocks of brittle building materials comprising the steps of feeding the blocks along a longitudinal path past a first scraping station having scraping irons of prestretched, thin flexible ribbon to remove thin surface layers from the transverse faces of the blocks; further feeding the blocks past at least one other scraping station having scraping irons of prestretched, thin flexible ribbon to remove additional thin surface layers fro mthe transverse faces; the ribbon of at least one of the stations having a wavy scraping edge, and oscillating the ribbon having the wavy scraping edge to obtain a decoration on the block faces while removing the respective thin surface layers.

2. The method according to claim 1 wherein the blocks are fed substantially contiguously, and all of the transverse faces are scraped simultaneously.

3. For accurate machining of the faces of blocks of brittle building materials, scraping means comprising a scraping iron of thin flexible ribbon; holding means stretching the ribbon, the holding means comprising a fixed support member, a resilient support member, the fixed support member and resilient support member defining 1- ribbon receiving means therebetween, and means to vary the force of the resilience of the resilient member; and means for feeding blocks of brittle building material past the scraping iron to remove end surface layers from the faces of the blocks.

4. The scraping means according to claim 3 wherein the ribbon is steel having a maximum thickness of 1 mm., and the ribbon is held perpendicular to the block faces to be machined.

5. For accurate machining of the faces of blocks of brittle materials, scraping means comprising a scraping iron of thin flexible ribbon; holding means stretching the ribbon, the holding means comprising a pair of winding drums about which the ribbon is wound, and a pair of holders receiving therebetween an intermediate part of the ribbon between the drums; and means for feeding blocks of brittle building material past the iron to remove thin surface layers from the faces of the blocks.

6. For accurate machining of the faces of blocks of brittle building materials, scraping means comprising a scraping iron of thin flexible ribbon having a wavy scraping edge; means for feeding blocks in a path past the iron; holding means stretching the ribbon against the faces of the blocks being fed past the iron to remove thin surface layers from the faces of the blocks, the holding means including means to permit oscillation of the ribbon transverse to the path of the blocks to produce decorative surfaces on the block faces.

7. A method for accurate machining of steam cured porous concrete building elements comprising the steps of: scraping successive thin surface layers from two opposite faces of the blocks with thin, prestretched flexible ribbon to obtain accurate, plane surfaces, contiguously feeding the blocks along a longitudinal path, with the planed surfaces engaging each other past a first scraping station having scraping irons of prestretched, thin flexible ribbon to remove thin surface layers simultaneously from all of the remaining transverse faces of the blocks; and further feeding the blocks past at least one other scraping station having scraping irons of prestretched, thin flexible ribbon to remove additional thin surface layers from the transverse faces, the pre-planed opposite faces forming support means for the adjacent blocks to prevent edged breakage thereof.

8. The method according to claim 7 wherein the scraping irons have a thickness of less than 1 millimeter, and the scraping irons are held perpendicularly to the faces of the blocks to be scraped.

References Cited in the file of this patent UNITED STATES PATENTS 133,893 Schleier Dec. 10, 1872 508,579 Ruch Nov. 14, 1893 670,698 Bodenstein Mar. 26, 1901 1,355,035 Collins Oct. 5, 1920 1,563,081 Funk Nov. 24, 1925 2,884,921 Drake May 1, 1959 FOREIGN PATENTS 1,001,300 France Oct. 24, 1951 1,129,695 France Jan. 24, 1957 

1. A METHOD OF ACCURATELY MACHINING THE FACES OF BLOCKS OF BRITTLE BUILDING MATERIALS COMPRISING THE STEPS OF FEEDING THE BLOCKS ALONG A LONGITUDINAL PATH PAST A FIRST SCRAPING STATION HAVING SCRAPING IRONS OF PRESTRETCHED, THIN FLEXIBLE RIBBON TO REMOVE THIN SURFACE LAYERS FROM THE TRANSVERSE FACES OF THE BLOCKS; FURTHER FEEDING THE BLOCKS PAST AT LEAST ONE OTHER SCRAPING STATION HAVING SCRAPING IRONS OF PRESTRETCHED, THIN FLEXIBLE RIBBON TO REMOVE ADDITIONAL THIN SURFACE LAYERS FRO MTHE TRANSVERSE FACES; THE RIBBON OF AT LEAST ONE OF THE STATIONS HAVING A WAVY SCRAPING EDGE, AND OSCILLATING THE RIBBON HAVING THE WAVY SCRAPING EDGE TO OBTAIN A DECORATION ON THE BLOCK FACES WHILE REMOVING THE RESPECTIVE THIN SURFACE LAYERS. 